Photographic sensitizer



Patented Nov, 3, 1925.

EDWIN ERNEST JELLEY, 0F MALVERN, SOUTH AFRICA.

PHOTOGRAPHIC SENSITIZER.

No Drawing.

To all whom it may concern i Be it known that I, EDWIN ERNEST JEL- Ln a British sub e-L't, and resident of Malvern, Natal, Union of South Africa, have invented certain new and useful Improvements in Photographic Sensitizers (for which]. have filed an application in England No. 17,507/24, dated22nd July, 1924), of which the following is a specification.

This invention relates to an improved sensitizer for photographic purposes, and has for its object to provide a sensitizer which may be stored indefinitely, and which may be applied when required to any suitable surface, such as paper, parchment, plaster, glass, textile fabrics, andfilms of casein, gelatine, albumen and the like, so that such surface may be rendeled sensitive to light, and prints may be produced thereon photographically.

Another object of the invention is to pro duce a sensitizer for application to surfaces in order to enable such surfaces to be utilized for printing out in the manner of existing self toning papers and also in the manner of gas light papers, whereby the period of exposure is reduced and the image may be developed subsequently in an alkaline solution.

A further object of the invention is to produce a solution which can act not only as a sensitizer but which may also be used as an intensifier for photographic plates, particularly Lumiere autochrome or other colour plates.

A still further object of the invention is to produce a sensitizer containing soluble salts .of silver, the sensitizing solution being adapted to soak into or impregnate the surface of the material to be sensitized.

Another object of the invention is to provide an improved method of sensitizing surfaces, whereby such surfaces will be rendered sensitive to light and whereby the surface after exposure may be developed in an alkaline solution'without the use of existing developers.

Surfaces coated with a sensitizer according to the invention are particularly suitable for printing photographs from negatives, for the production of light prints, (for which purpose ferrotype paper is now usually used), for use in taking finger Application filed. August 11, 1924. Serial No. 731,490.

prints, and for the production of sul hur prints in steel examination; but it will be understood that surfaces coated according to the invention may also be used for obtairlung photographic reproductions in genera In the production of sensitized surfaces or films for photographic purposes it has been suggested previously to coat the surface or film with an emulsion formed of one or more silver halides to which was added a suitable neutral salt of hydrazine or compound or derivative of hydrazine, excludmg the aromatic compounds of hydrazine or hydroxylamine, or the surface or film sensit zed in the usual way with an emulsion containing insoluble salts of silver'was immersed in a solution of the hydrazine salt or derivative, the amount of the hydrazine salt or derivative used being determined by the reducing action of the said salt, it being assumed that each molecule of hydrazine hydrate is capable of reducing four mole cules of silver halide.

According to the present invention a soluble salt of silver is mixed with one or more of the soluble salts of hydrazine and/or its derivatives, and the solution containing these two salts may be applied by means of a brush or in any other convenient manner to the surface to be sensitized. If the surface is permeable to moisture, the solution will soak into and impregnate it. If the surface is impermeable, as in the case of glass for example, the surface is first coated with gelatine', albumen or the like whereupon the solution, 'according to the invention, is applied thereto. These soluble salts are either in the dry state and adapted to be mixed subsequently with sufiicient water to contain the said salts from 5% up to saturation, or they are kept in solution of a strength such that it contains the salts each in a proportion of from 7 up to saturation.

The soluble salts, of silver that have been found to give satisfactory results are silver nitrate, silver lactate, silver chlorate, silver flouride, silver formate, silver acetate and silver sulphate, whilst the hydrazine derivatives that may be used include the mono and di-acid nitrates, flourides, lactates,

formates, acetates and sulphates and the mono-chlorate of h drazine, and of monoalk l anddi-alkyl iydrazines, soluble acyl an di-acyl hydrazines, urazole, and soluble salts, such as the nitrate, of semi-carbazide and its alkyl derivatives any of which may be used either separately or two or more thiareof together, for mixing with the silver sa ts.

A preferred solution for coatingasurface to be rendered sensitive to light consists of about l parts by weight of silver nitrate, about 4 parts by weight of hydrazine acid nitrate N 11, nuon dissolved in about 92 parts by weight of water. The hydrazine acid nitrate is preferably prepared by double decomposition between hydrazine sulphate and barium nitrate.

It has been found that when the percentage of soluble silver salt in the sensitizing solution is below 5%, the prints produced are pale or poor. Whenthe percentage of soluble silver salt is below 4% any imperfeet-ions in the paper or other-surface to be coated are liable to produce irregularities in the finished print, these irregularities becoming more prominent the lower the percentage of the soluble silver salt. When the solution contains from about 4% up to about 10% of the soluble silver salt the best results are obtained. With more than 10% of the soluble silver salt in solution the results become inferior owing to the fact that the excess of silver salt merely crystalizes on the surface and produces a granular or mottled appearance when the surface is developed as hereafter described; the additional amount may also be regarded largely as Waste of silversalt.

For good results in development, the amount of the salt of hydrazine or its derivatives must be in excess of 2%. The best proportions, calculated as hydrazine acid nitrate, are 2% plus an amount numerically equal to one half of the percentage of silver salt, calculated as nitrate. Thus a sensitizer containing 4% of silver nitrate gives satisfactory results on development when the amount of hydrazine acid nitrate is not less than 4%. However the percentage of hydrazine salt or its derivatives may be increased to saturation without deleterious efl'ect, but it does not improve the result obtained and therefore the excess may be regarded as waste.

Where however the amount of silver nitrate used amounts to say 10% the amount .of hydrazine salt would be 7%. In such a case the amount of hydrazine salt above 4% would not be waste but is necessary for the purpose of reducing the larger amount of silver salt.

The silver salts used for the production the fluoride of silver and of hydrazine quickly decomposes in glass bottles, although it may be stored for a short time in waxcoated glass bottles. A solution containing the fluoride of silver and of hydrazine has, however been found to give results substantially equivalent to those obtained with a solution containing the nitrates of these substances. The organic salts of silver, namely the lactate, formate, and acetate, in conjunction with the corresponding salts of hydrazine gradually undergo spontaneous decomposition, with deposition of metallic silver. A mixture of the chlorates of silver and hydrazine is very gradually decomposed with evolution of nitrogen and deposition of metallic silver and silver chloride. Consequently solutions of the lactates, fluorides, formates, acetates, or chloratcs of silver and of hydrazine are not capable of being stored for indefinite eriods as is the case with a solution containing the silver nitrate and hydrazine acid nitrate. A's silver sulphatev is only soluble to the extent of 0.74% in water, a solution containing silver sulphate is inferior to a solution containing silver nitrate but is suitable for the production of pale prints.

Of the salts of hydrazine and its derivatives, hydrazine acid nitrate V am-( o.

has been found to produce the most favourable results when used in conjunction with silver nitrate. Hydrazine mono-nitrate also gives satisfactory results, but a sensitizing solution containing this salt is'very sensitive to alkalies, so that a deposition of metallic silver very gradually takes place in glass bottles owing to the alkalinity of the glass. The acid nitrates of the mono and di-alkyl hydrazines, especially methyl and ethyl, di-methyl and di-ethyl, hydrazines when in solution with silver nitrate. produce substantially the same result as a solution of hydrazine acid nitrate and silver nitrate. The salts of the aliphatic alkyl and di-alkyl hydrazines however are more expensive than corresponding salts of hydrazine.

The soluble mono-acyl, and di-acyl hydrazines, such as di-acetyl hydrazine, gradually hydrolysedurin storage in solution and is present the mixture ultimately becomes amixture of silver nitrate and a salt of hydrazine.

' alkyl derivatives and urazole if applied to '15 in proportions chemically equivalent to the Salts of' semiearbazide and its alkyl derivatives and urazolewhen in solution with silver nitrate also have inferior keeping properties compared with hydrazine acid nitrate. Solutions containing soluble monoacyl and di-acyl hydrazines, soluble salts such as the nitrate of semi-carbazide. and its the surface to be sensitized directly after the preparation of the solutions give satisfactory results. The aromatic hydrazines readily decompose in solution especiall in con- 'junction with the solublesilver sa ts.

Satisfactory results may also be obtained by using methyl. hydrazine. acid nitrate,

symmetrical and unsymmetrical di-methyl' hydrazine acid nitrates, ethyl hydrazine ac1d nitrate, symmetrical and unsymmetrical diethyl hydrazine acid-nitrates instead of hydrazine acid nitrate, these salts being used proportion of hydrazine acid nitrate calculated in the manner above described.

The soluble salts of silver and of hydrazine or its derivatives may also housed and stored in the dry state, either loose or compressed into tablets, the two salts being either separate or mixed together in the required portions so that it is only necessary to add the necessary amount of water to form the sensitizer. The dry salts or tablets are dissolved in the necessary quantity of water so as to produce a sentitizing solution'containing from up to saturation of these salts. For example, a tablet containing 2 grms. silver nitrate and 2 grins. hydrazine acid nitrate, is dissolved in 46 0. cm. of water the resulting solution then containing 4% of each of the two salts.

Any water absorbent surface free from reducing, oxidizing, alkaline, or sulphide compounds may be used for obtaining photographic reproductions thereonv provided .that the surface contains a minute trace of a halogen salt. such as sodium chloride or bromide. Ordinary papers of commerce, such as note,. drawing or typing paper, usually contain small proportions of halogen salts but such papers are preferably soaked, before the sentitizing solution is applied thereto, in a solution containing a halogen salt such as sodium chloride or potassium bromide to an extent of between and 1% by Weight, and then dried. Textile fabrics, plaster or other surfaces are also treated with a Weak saline solution as above described, before treatment with the sen sitizing solution. The trace of halogen salt required in the material is so small, that, in

the case of paper, it could be added at the time of its manufacture, and would not intcrfere with any of the ordinary uses of ing to the present invention is applied to the surface to be rendered sensitive to light, and allowed to dry in the air, or. if desired the drying may be aided by means of a gentle heat; The coating and drying is Jerformed in a dull light, preferably a yeflow glass,

safe-light such as is used for bromide and gas light papers. Photographs may then be printed on the material treated'in this man ner in either of two ways, that is to say Either the surface is ex in the same way as with existing sel -t0ning pa rs, or

else it is given a brief exposure, so t at the deepest shadows are only justfaintly visible, and is then develop and fixed. Ac-

cording to the first method the image is rinted from a negative or the like in sunight or arc-light until the print is much deeper in tone than is required in-the finished print (as is usual with self-toning papers), and then the image is fixed in a 10% solution of hypo. (Sodium thiosulphate). The prints thus obtained are of a sepia-brown shade, but if desired may be tonedprior to fixing, to a deep purple black by means of the usual gold toning bath.

According to the second method the paper or other material sensitized according to the invention, is exposed through a negative, until a very faint outline of the image appears. With a normal negative this requires an exposure of five seconds to sunlight, or the light from the combustion of about 10 cms. of magnesium ribbon. Any other actinic light, however, may be used. The number of different combinations of substances that may be used to develop such an image is very large and'in general it may be stated that the developer contains two components in solution, namely an alkali, and a salt that will, by double decomposition, convert all the free silver nitrate on the sensitized surface intoan insoluble silver salt. Of the many developers that have been foundto give satisfactory results may be mentioned a solution consisting of- Parts by weight. Sodium chloride 2.0 Sodium hydroxide -4 0.2

Water 97.8

papers.

Parts by weight. D1-sodium hydrogen phosphate 5 Sodium carbonate cr vstals l 5 \Vater 90 Many salts of weak acids, such as sodium acetate, act as developers when in hot aqueous solution. In the developers above described the salt of hydrazine (or its derivative) is the actlve reducing agent. \Vith such a developer the image may be developed in about twenty seconds, and the paper or.other surface may be placed direct into the fixing bath of hypo, the fixing tale ing about one or two minutes. The print is then washed and dried. The drying may be aided by heat if desired. Materials sensitized and exposed'as above described may also be developed with any of the existing non-staining developers in "use for gaslight and bromide paper but these offer no s ecial advantages. Prints produced in his w manner are normally of a cold brown shade,

' print through intermediate shades, to chalky red tones. Black or 'grey tones are obtained by first bleaching the print in the following solution: Mercuric chloride, 1 gramme; hy-

drochloric acid, 1 gramme; water suflicient.

to make 500 c. cm. 'of solution and then washing the print and immersing it in a 5% solution of sodium sulphite. In addition prints prepared according to the present invention maybe dye-toned by any of the existing processes applicable to bromide \Vhen light acts on'a surface sensitized in the manner above described, the first chemical change that takes place is the formation of a minute trace of a silver sub-salt. Thus if the material coated contains a trace of sodium chloride, then silver sub-chloride is formed, the free chlorine forming silver chloride with some of the silver nitrate which has not been converted into silver chloride on coating the surface, with simultaneous oxidation of a portion of the salt of hydrazine (or its derivatives). If the exposure to light is stopped at this stage, only the deepest shadows in the picture are faintly visible. If, the print is then immersed in an alkaline sodium chloride developer, an almost instantaneous conversion of the remaining silver nitrate into the insoluble sil- 1,5oo,24o l ver chloride takes place. The hydroxide in the developerliberates the hydrate of hydrazine (or its derivative),.which, acting in conjunction with the remaining free alkali converts the silver sub-salt (silver sunchloride) into metallic silver. The minute particles of metallic silver thus formed act as nuclei on which is deposited metallic silver formed by the reducing action of the hydrazine hydrate on the silver chloride. In this manner a silver image is built up on the original very faint image of silver subsalt. W hen, however, the paper isused as a printing out paper, the printing is prolonged and the silver sub-salt is in turn converted into metallic silver, whilst an additional amount of normal halogen salt is formed from the 'free silver nitrate with simultaneous oxidation of the salt of hydrazine or. its derivative. Thus the trace of halogen salt originally present in the surface treated acts catalytically under the prolonged influence of light, causing reduction of the silver salt at the expense of oxidation of the hydrazine salt or its derivative.

The property: of the sensitizer to deposit silver on silver nuclei enables it to be used as an intensifier of photographic plates, es-

pecially Lumiere autochrome and similar types of colour plates. Vhen the sensitizer is to be used for this purpose, all that is necessary is to dilute 1 part by volume of the sensitizer with 9 parts by volume of distilled water. The deposition of metallic silver on the photographic image is considerably accelerated. b the addition of from 1% to 10% of so ium acetate. After intensification the plate is fixed and washed in the usual manner.

A sensitizing solution formed as above described may be stored for practically any length of time, evenwhen exposed to light, or in hotclimates, and is always ready for application to the surfaces to be treated so that it is only necessary to treat the surface with the solution when it is required for use. A convenient way of applying the mixture to the surface to be sensitized is by means of a small brush, but the coating may be performed with any suitable device such as roughened or ground glass rollers or rubber or any other suitable rollers which produce an even and uniform coating on the surface. 10 c. cm. of the solution have been-found sufiicient to coat about 45 pieces of paper 8x10 cm.

By the use'of soluble salts of hydrazine or its derivatives it is possible to use soluble silver salts as sensitizers for paper,

nitelythus presenting great advantages over compound necessary for such development. Furthermore the sensitlzer may be used at will as an intensifier. Not/only is the actual 'cost of photographic paperconsiderably reall existing developers.

A sensitizer according to the present 1nvention has various advantages over sensi- 'tizers at present in use. 'For example the solution may be applied by unskilled persons as it is not in the form of an emulsion, and paper or surfaces for printing purposes are considerably cheaper than ordinary printing papers while being capable .of being stored for the same periods as the usual papers on the market. 'lhe-sensitizcr when made up either in the form of powders or tablets or in solution can be kept. indefinitely and the solution-can be applied to a surface on which a photograph is to be reproduced whenever required.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is 1. A sensitizing agent for the purpose set forth, consisting of a mixture of a soluble salt of silver and a soluble salt of the hydrazine group.

2. A sensitizing agent for the pur ose set forth, consisting of a mixture of si ver nitrate and a soluble salt of the hydrazine group.

3. A sensitizing agent for the purpose set forth, consisting ofa mixture of a soluble salt of silver and soluble salts of the hydrazine group.

4. A sensitizing agent for the purpose set forth, consisting of a mixture of silver nitrate and soluble salts of the hydrazine group.

5. A sensitizing agent for the purpose set forth, consisting of a mixture of silver nitrate and hydrazine acid nitrate.

6. A sensitizing agent for the purpose set forth, consisting of dry silver nitrate and dry hydrazine nitrate, adapted to be mixed with sutficient Water to form a solution containing about 4% of each of said salts.

7 A sensitizing agent for the purpose set forth, consisting of a solution containing a soluble salt of silver, a soluble salt of the hydrazine group, and water, the solution being such that it contains about 4% of the soluble silver salt and 4% ofthe soluble salt of the hydrazine group.

8. A sensitizing agent for the purpose set forth, consisting ofa solution contaming a soluble salt of silver, soluble salts of the hydrazine group, and water, the solution being such that it contains about 4% of the soluble silver salt and 4% of the soluble salts of the hydrazine group.

9. A sensitizing agent for the purpose set forth, consisting of an aqueous solution containing at parts by weight of silver nitrate,

4 parts byweight of hydrazine acid nitrate, and 92 parts by weight of water. 10. A sensitizing a trate,-tparts by weight of a soluble salt, of the hydrazine group, and 92 parts by Weight of water. a

11. A sensitizing agent for the purpose set forth, consisting of an aqueous solution containing 4 parts by weight ofsilver nitrate, 4 parts by weight of soluble salts of the hycut for the purpose set forth, consisting 0 an aqueous solutloncontaining 4 partsby weight of silver nidrazine group, and 92 parts by weight of water.

12. A sensitizing agent for the purpose set forth, consisting of a soluble salt of silver which has a solubility of atleast in water and a soluble salt of the hydrazine group.

13. A sensitizing agent for the urpose set forth, consisting of a soluble sat of silver which has a solubility of at least 5% in .-water and soluble salts of the hydrazine group.

14. A sensitizing agent for the purpose set forth, consisting of silver nitrate, hydrazine acid nitrate and water. i

"15. 'A sensitizing agent for the urpose set forth consisting of a solution 0 a soluble salt of silver and a soluble salt of a hydrazine, the solution containing at least 4% ofeach of said salts.

16. A method of rendering paper, parchment, plaster, glass, textile fabrics, films of casein, gelatine and albumen, and so forth sensitive to light, consisting in coating the surface of said substances with an aqueous solution of a soluble salt of silver and of a soluble salt of the hydrazine group.

17. A method of rendering paper, parchment, plaster, glass, textile fabrics, films of casein, gelatine and albumen, and so forth sensitive to light, consisting in coating the surface of said substances with an aqueous solution ofa soluble salt of silver and soluble salts of the hydrazine group. 4 18. A method of sensitizing paper, parchment, plaster, glass. textile fabrics, films of casein, gelatinc and albumen, and the like, consisting in impregnating said substances with a solution consisting of water, silver nitrate and hydrazine acid. nitrate.

19. A method of rendering surfaces containing traces of halogen salts sensitive to light, consisting in treating said substances with a solution'consisting of a soluble salt of silver and of a soluble salt of the hydrazine group.

20. A method of rendering surfaces containing traces of halogen salts sensitive to light, consisting in treating said substances with a solution consisting of a soluble saltof silver and of soluble salts of the hydrazlne I 21. A method of sensltizingsurfaces containing traces of halogen salts, consisting in said surfaces with a 50111171011 coating said surfaces with a solution consisting of 4; parts by weight of silver'nitrate, 4 parts by weight of hydrazine acld nltrate, and 92 parts by weight of water. i

24.- A method of treating surfaces for photographic purposes consisting in soaking said surface in a weak saline solution so as to impregnate said surface \vith'small tracesofhalogen salts, coating the surface thus treated with an a ueous solution of a soluble a compatible salt of the printing an image on said oping said image.

salt of silver an hydrazine group, surface, and deve '25. A method of treating surfaces for photographic purposes consisting 1n soak-' ing said surface in a weak saline solution so of sensitizing surfaces con on said surface and sodium thiosulphate.

as to impregnate said surface with small of the hydrazine group, printing an image on said surface, and developing said image in an alkaline solution.

26. A method of treating surfaces for photographic purposes consisting in soaking said surface in a weak saline solution so as to impregnate said surface withsmall traces of halogen salts, coating the surface thus treatedwith an aqueous solution of a soluble salt of silver and a compatible salt of the hydrazine group, printing an image on said surface, and developing said image in a sodium chloride solution containing a small amount of caustic alkali, whereby the soluble salt of the hydrazine group acts as a reducing agent to effect the development of the latent image.

.27. A method of treating surfaces for photographic purposes consisting in soaking said surface in a weak saline solution so as to impregnate said surface with small traces of halogen salts, coating the surface thus treated with an aqueous solution of a soluble salt of silver and a compatible salt of the hydrazine grou printin an image EDWIN ERNEST JELLEY.

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